ISALPHA(3) Library Functions Manual ISALPHA(3)

isalpha — alphabetic character test

Standard C Library (libc, -lc)

#include <ctype.h>

int
isalpha(int c);

The () function tests for any character for which isupper(3) or islower(3) is true. The value of the argument must be representable as an unsigned char or the value of EOF.

In the ASCII character set, this includes the following characters (preceded by their numeric values, in octal):

101 ``A'' 102 ``B'' 103 ``C'' 104 ``D'' 105 ``E''
106 ``F'' 107 ``G'' 110 ``H'' 111 ``I'' 112 ``J''
113 ``K'' 114 ``L'' 115 ``M'' 116 ``N'' 117 ``O''
120 ``P'' 121 ``Q'' 122 ``R'' 123 ``S'' 124 ``T''
125 ``U'' 126 ``V'' 127 ``W'' 130 ``X'' 131 ``Y''
132 ``Z'' 141 ``a'' 142 ``b'' 143 ``c'' 144 ``d''
145 ``e'' 146 ``f'' 147 ``g'' 150 ``h'' 151 ``i''
152 ``j'' 153 ``k'' 154 ``l'' 155 ``m'' 156 ``n''
157 ``o'' 160 ``p'' 161 ``q'' 162 ``r'' 163 ``s''
164 ``t'' 165 ``u'' 166 ``v'' 167 ``w'' 170 ``x''
171 ``y'' 172 ``z''

The isalpha() function returns zero if the character tests false and returns non-zero if the character tests true.

The 4.4BSD extension of accepting arguments outside of the range of the unsigned char type in locales with large character sets is considered obsolete and may not be supported in future releases. The iswalpha() function should be used instead.

ctype(3), isalnum_l(3), islower(3), isupper(3), iswalpha(3), ascii(7)

The isalpha() function conforms to ISO/IEC 9899:1990 (“ISO C90”).

July 17, 2005 macOS 15.2